Actually a properly set mushroom anchor holds very well.
The key is scope.
If you are in 10 feet of water and only have 30 feet of line don't use a mushroom!
To set a mushroom the shaft has to be lying flat on the bottom and the "mushroom" of the anchor has to dig into the mud, if the shaft bounces up and down then the anchor will lose its hold. (that's where the scope comes in)
If you're boating on Winni you really should have more than 30' of line on board
BTW I also carry two Danforth clones, as I said I only use the mushroom as a lunch hook on a muddy or sandy bottom in calm conditions!